The document is a chemistry class lecture on trends in the periodic table, specifically electronegativity. It defines electronegativity as an atom's ability to attract electrons in a chemical bond. It then explains that electronegativity increases from left to right across periods due to more protons, but decreases down groups because more electron shells shield the nucleus from outer electrons. Practice problems are assigned for students to study these trends.

1. Launch: 9/25
 Grab your binder and immediately take a seat
 Place Textbook HW on desk
5. The chart below shows the relationship between
the first ionization energy and the increase in
atomic number. The letter on the chart that
represents the noble gases is:
a. W
b. X
c. Y
d. Z

2. What is the trend for
electronegativity?
Mr. Heffner
9/25/09

3. Review: Atomic Radius
Decreases
Increases

4. IV. Ionization Energy
Increases
Decreases

5. V. Electronegativity
A. What is electronegativity?
1. The ability of an atom to attract electrons toward itself
in a chemical bond
H
O
H

6. V. Electronegativity
B. What is the trend for electronegativity?
1. Electronegativity increases across a period (LR)
i. As the number of protons increases, the nucleus gets
stronger and pulls all nearby electrons towards it

7. V. Electronegativity
B. What is the trend for electronegativity?
2. Electronegativity decreases down a group (TopBottom)
i. As the number of electrons increases, more rings are added
ii. The inner rings shield other electrons from the attractive
forces of the nucleus

8. V. Electronegativity
Increases
Decreases

9. Practice Questions
 See Periodic Trends Worksheet

10. Homework
 Study for Monday’s Unit #2 Exam!
 Look over Quiz #3
 Look over Exit Slips
 lpschem.wordpress.com

11. Exit Slip
1. Electronegativity is the
a. energy it takes to remove an electron from an atom.
b. number of protons and neutrons in an atom.
c. ability of an atom to attract electrons toward itself in
a chemical bond
d. distance from the nucleus to the valence ring.

12. Exit Slip
2. In general, how does electronegativity vary
throughout the periodic table?
a. it decreases across a period from left to right, and
decreases down a group from top to bottom
b. it increases across a period from left to right, and
increases down a group from top to bottom
c. it increases across a period from left to right, and
decreases down a group from top to bottom
d. It decreases across a period from left to right, and
increases down a group from top to bottom

13. Exit Slip
3. Why does electronegativity decrease down a group?
a. Because atomic radius decreases
b. Because the nucleus is shielded by the inner rings
c. Because the outer electrons are more strongly
attracted by the nucleus
d. Because the trend for electronegativity increases
down a group

14. Exit Slip
4. Which of the following atoms is more
electronegative than S?
a. oxygen (O)
b. phosphorus (P)
c. selenium (Se)
d. magnesium (Mg)

15. Exit Slip
5. Which of the following atoms is the most
electronegative?
a. sodium (Na)
b. phosphorus (P)
c. selenium (Se)
d. magnesium (Mg)